Essentially all electrical codes for industrial and residential wiring require the use of a grounding wire for all circuits. This requirement applies to outlet receptacles, such as wall plugs, and the units installed therein have provisions for receiving a grounding prong from any electrical appliance, tool, etc., to be energized at that outlet. As a further safety factor, most appliances, tools, etc., are now provided with a three-wire cord and plug, with the ground wire being attached to the case of the unit, whereby the case is connected to the circuit ground during use. This prevents shocks to an operator in the event of an insulation failure.
One electrical appliance, however, that has not been adapted for a ground wire is the incandescent lamp socket as utilized for table lamps, floor lamps, pull-down lamps and the like. A conventional cap-and-shell socket unit has been universally utilized for these devices in an essentially constant form for many years. See, for example, U.S. Pat. No. 2,001,317 issued to F. W. Slady on May 14, 1935. These cap-and-shell units often enclose one of several types of switches for energizing the lamp socket; e.g., key type (2- or 3-way), pull chain or push type. A thin insulating layer is used to separate the switch-socket member from the metallic enclosure. After extended use, or due to excessive heating from the lamp, the insulation may become charred, brittle or otherwise become ineffective. Alternatively, electrical leads may become loose and penetrate the insulation in some manner. When such failures occur, a person operating the lamp switch may be subjected to an electrical shock.
Only one cap-and-shell lamp socket is known which provides for the attachment of a ground wire. It is described in U.S. Pat. No. 1,974,049, issued to H. Hubbell, Jr., on Sept. 18, 1934. In that prior art unit, a terminal with a threaded screw is provided within the cap. This terminal is formed from a separate insert within the cap. Such a construction necessitates a modified insulation construction, cannot be installed in an already fabricated socket unit, and is relatively costly. It is probably these reasons that have prevented commercialization.
Accordingly, it is an object of my invention to provide a lamp socket unit that may be easily grounded through the attachment of a ground wire.
It is another object to provide a method of grounding a lamp socket unit that may be provided for in the manufacture of lamp socket units as well as in units already fabricated.
It is still another object to provide a tool for the fabrication of grounding means for a cap-and-shell type socket unit and for effecting the attachment of a ground wire therein.